Report to trace if free(NULL) is called, which was not expected before

Signed-off-by: Juergen Kosel <juergen.kosel@softing.com>

src/Heap.c

@@ -254,6 +254,10 @@ void myfree(char* file, int line, void* p)
 			free(((int*)p)-1);
 		Thread_unlock_mutex(heap_mutex);
 	}
+	else
+	{
+		Log(LOG_ERROR, -1, "Call of free(NULL) in %s,%d",file,line);
+	}
 }